Circuit-switched network architectures, such as those based on synchronous optical network (SONET) or synchronous digital hierarchy (SDH) standards, were originally designed to support voice traffic using dedicated fixed-bandwidth connections. Although such networks are advantageous in that they incorporate substantial reliability and protection mechanisms, their primary disadvantage has been a lack of bandwidth efficiency.
Packet-switched network architectures, which include those based on asynchronous transfer mode (ATM) or Internet protocol (IP) standards, have traditionally been much better able than circuit-switched architectures to handle data traffic. Since data traffic is inherently bursty, it leads to underutilization of the fixed-bandwidth connections of conventional circuit-switched networks. Packet-switched network architectures provide the benefits of statistical multiplexing, which allows for better handling of bursty data traffic.
Recently, virtual concatenation (VC) and link capacity adjustment scheme (LCAS) protocols have been developed which allow more efficient use of the existing fixed-bandwidth connections associated with circuit-switched SONET/SDH network infrastructure. For example, these protocols are utilized in transmission of Ethernet over SONET (EoS) data traffic over metropolitan networks, and in numerous other data transmission applications. The VC and LCAS protocols are described in greater detail in, for example, ITU-T standards documents G.707 and G.7042, respectively, both of which are incorporated by reference herein.
Virtual concatenation generally allows a given source node of a network to form a virtually-concatenated group (VCG) which includes multiple members each associated with a corresponding data stream. The different data streams may then be transmitted over diverse routes through the network from the source node to a given destination node. The destination node recombines the streams to reconstruct the original VCG.
The LCAS protocol enhances the basic virtual concatenation functionality described above by allowing so-called “hitless” addition and deletion of members from a VCG, that is, addition and deletion of members without the introduction of errors into the transmitted data. The LCAS protocol also enables a VCG to operate at a reduced capacity after the failure of routes associated with one or more members, by allowing the temporary removal of members associated with failed routes from the VCG.
The above-cited U.S. patent application Ser. No. 10/446,220 and Ser. No. 10/745,881 provide additional performance improvements beyond those associated with the conventional VC and LCAS protocols.
When implementing VC or LCAS related techniques, it is often necessary to provide compensation for differential delays of the diverse routes over which the various members of a VCG are transmitted. Unfortunately, providing such a capability in conventional practice typically requires that each network node be configured to include an expensive, high-capacity differential delay buffer. Since a given destination node may receive different diversely-routed members at different times, the differential delay buffer is used to store member data until all members are received and the original data stream can be properly reconstructed.
Additional details regarding conventional aspects of differential delay compensation can be found in, for example, G. Garg et al., “Managing Differential Delay in SONET Architectures,” EE Times, January 2002, which is incorporated by reference herein.
The cost of upgrading an entire network with differential delay buffers is often prohibitive. As a result, most service providers will not upgrade their complete network all at once to support data services using VC and LCAS, but will instead phase these capabilities in over time.
A drawback of conventional techniques is that they are not specifically designed to provide a desired level of differential delay compensation in situations in which only a subset of the network nodes includes differential delay buffers.
A further complication arises from the fact that several source-destination traffic demands may share the same differential delay buffers. Thus, when routing a given data stream using virtual concatenation over diverse paths, the routing algorithm needs to determine the current utilization of the relevant differential delay buffers. Not all sets of diverse paths may be feasible, since one or more of the sets of diverse paths could result in a differential delay that cannot currently be compensated by the available buffer space.
Accordingly, a need exists for improved route determination techniques for virtually-concatenated data traffic, which are capable of providing desired levels of differential delay compensation in situations in which differential delay buffers are incorporated into only a subset of the network nodes.